Batman: Arkham City is the sequel to Batman: Arkham Asylum and once again stars the masked superhero Batman as the protagonist. The game takes place a year and a half after the events of the original game. After Joker was stopped from taking over the asylum, the asylum's former warden Quincy Sharp claims the responsibility for having averted disaster and he uses the popularity to become mayor of Gotham City. To suppress crime further, an enormous open-air prison called Arkham City is built. Citizens (as well as journalists in particular) are under strict supervision and the slightest disturbance is sufficient to be transferred to the prison. Sharp is assisted by psychiatrist Hugo Strange and hires the armed forces of the rogue security firm TYGER Security to maintain order. The story for Batman starts when he, as Bruce Wayne, is sent to Arkham City after declaring his opposition to the facility in a press conference. Strange is aware of Wayne's dual identity, but he can escape from the Penguin and gets his gear back through an airdrop from Alfred Pennyworth, which allows him to turn into Batman and fight the facility from the inside. Much of the story also revolves around a strange disease called the Titan formula that has infected Joker, and a secret plan called Protocol 10. Other famous characters from the franchise that make an appearance include Catwoman, Mr. Freeze, Rā's al Ghūl, and Clayface.